The purpose of this workshop is to define the current knowledge of osteoarthritis and its pathophysiology. Specific areas to be addressed will include: clinical and epidemiological aspects, specific alterations and etiopathogenesis of changes in joint tissues particularly cartilage and subchondral bone, the roles of mediators and the induction of inflammatory episodes in osteoarthritis, repair mechanisms, and validation of biochemical markers for the diagnosis and/or monitoring of progression and treatment of the disease. The overall objective of this workshop is to increase the interdisciplinary exchange of novel ideas among orthopaedic surgeons, rheumatologists, epidemiologists, pathologists, bioengineers, cell biologists, biochemists and other basic scientists and to provide a forum for the evaluation and interpretation of the most recent research advances. This will define significant advances in the understanding of the etiopathogenesis of osteoarthritis and identify future research directions. This workshop will advance understanding and improve prevention and treatment of the most prevalent acquired connective tissue disorder that affects the diarthrodial joint. Working sessions of the meeting will include presentations by a select group of invited participants of their previously submitted manuscripts combined with in-depth discussions. These will be followed by breakout groups in which areas of critical concern (definition of gaps in knowledge and future research directions) will be defined. As an additional stimulus to future research, a publication in an orthopaedic/rheumatology journal summarizing the current state of knowledge and avenues for future investigation is also planned. In addition, a full length book containing the submitted and edited manuscripts together with the pertinent contributions during the breakout discussion is also planned. This summary of the proceedings and recommendations will be presented to NIAMS. This workshop represents a continuum of a format established jointly by the NIH and AAOS to address critical areas of concern in musculoskeletal disease.